1. Field of the Invention
This invention relates to thermocouples, and more particularly to a renewable thermocouple that can provide a continuous measuring tip upon erosion of the measuring tip end of the thermocouple.
2. Description of the Prior Art
Thermocouples utilize the principles of thermoelectricity by providing a circuit that includes two dissimilar metallic conductors joined together at one end to define a first, or hot junction, and a second, or cold junction. The temperature difference between the respective ends of the thermocouple will cause a current to flow in the circuit. In the past, the hot junction, or the measuring tip end of the thermocouple, was a mechanical joint of the two dissimilar metals. Consequently, if the joint was eroded away, the erosion would destroy the measuring tip, thereby requiring that the thermocouple be replaced with another. However, such repeated replacement is expensive where the measuring tip is exposed to continuous or intermittent erosive forces.
In U.S. Pat. No. 2,829,185, which issued Apr. 1, 1958, to J. Macatician et al., there is disclosed a thermocouple structure for use in a gun barrel for sensing the temperature of the interior surface of the bore of the barrel. The measuring tip of the thermocouple disclosed in that patent includes two dissimilar metals that are separated from each other by an insulating material. One of the thermocouple elements is a flat ribbon of nickel wire, and surrounding the nickel wire is mica insulation, against the outer surfaces of which the second thermocouple element is securely attached. An electrical connection between the dissimilar metals at the measuring tip is effected by grinding the measuring tip end of the thermocouple to provide metal particles that bridge across the surface of the intervening insulation to provide an electrical connection between the two dissimilar metals. However, the structure disclosed in that patent has several disadvantages in that it requires a flattened wire as one of the thermocouple elements, and the application of mica sheet insulation to the exterior surface of the flattened wire is a time consuming process. Further, the second thermocouple element is defined by a thick, machined, two-part thermocouple element that is both costly to produce and time consuming to assemble.
It is therefore an object of the present invention to provide an improved thermocouple structure in which the measuring tip of the thermocouple is self renewable in order to avoid the need for repeated replacement of thermocouple elements, and which structure involves minimum manual assembly procedures, is suitable for mass production, has a longer overall length to provide a continuous measuring tip as the thermocouple measuring tip structure is eroded in use, and can be made in a small size.